Turkish President Recep Tayyip Erdogan said on Saturday that US leader Donald Trump assured him there would be no American sanctions over Ankara's purchase of the Russian S-400 missile defence system, contrary to the stance taken by Washington so far. "We have heard from him personally that this would not happen," Mr Erdogan said after bilateral talks with Mr Trump at the G20 summit in Japan. "We are strategic partners with the United States. As strategic partners, nobody has the right to meddle in Turkey's sovereign rights. Everyone should know this." The Nato allies have been at odds over Turkey's decision to procure the S-400 system, with the US saying it was not compatible with alliance's defence network and could compromise its Lockheed Martin F-35 stealth fighter jets, an aircraft Turkey is helping to build and planning to buy. Turkey refused to back down on the purchase, with delivery scheduled to start in July, despite the possibility of expulsion from the F-35 programme. Washington has already halted the training of Turkish pilots on the aircraft in the US. But, sitting alongside Mr Erdogan before their talks, Mr Trump told reporters Turkey had been treated unfairly over its decision to buy the S-400s and blamed the "mess" on the administration of former president Barack Obama. However, he did not explicitly rule out sanctions and said the issue was a "two-way street" and both sides were evaluating "different solutions". “They wouldn’t let [Mr Erdogan] buy the missile he wanted to buy, which was the Patriot,” Mr Trump said. “You have to treat people fairly. And I don’t think he was treated fairly.” The US has sought to sell Ankara the Patriot air defence missile since at least 2013, but Mr Erdogan insisted it come with a transfer of technology so that Turkey can develop and build its own missiles. The Obama administration refused. Turkey's earlier quest for a Chinese missile system instead of the Patriot also fell through over technology-transfer conditions. Russia's Interfax agency on Saturday quoted Kremlin spokesman Dmitri Peskov as saying the S-400 deal with Turkey envisaged a partial handover of technology. Mr Trump said Mr Erdogan had paid "a tremendous amount of money upfront" for the F-35 to aircraft maker Lockheed, “and now he wants delivery”. "And now they’re saying he’s using the S-400 system, which is incompatible with our system, and if you use the S-400 system, Russia and other people can gain access to the genius of the F-35.” “So it’s a mess,” he said. “And honestly, it’s not really Erdogan’s fault.” Mr Erdogan's remarks after their talks echoed Mr Trump's argument. "We have a payment so far of $1.4 billion to the United States," he said. "As joint producers, until now four F-35 jets have been delivered to us, but we will still receive... a total of 116 jets. We are expecting these," he added. "What some people in lower ranks are saying absolutely do not align with Mr Trump's approach. I believe these will not harm our bilateral ties, and that is the commitment we are going on with." Turkey had put its hopes on the relationship between Mr Erdogan and Mr Trump to protect it from repercussions from the S-400 deal. Their meeting in Osaka was seen as a last push to avoid US sanctions that could significantly damage Turkey's already ailing economy. However, Mr Erdogan's account of their exchanges appeared to go beyond statements made by the Turkish presidency and the White House after the talks, which lasted around 40 minutes. The White House said Mr Trump "expressed concern" over the S-400 deal and "encouraged Turkey to work with the United States on defence co-operation in a way that strengthens the NATO alliance", while the Turkish presidency said only that Mr Trump had voiced a desire to resolve the dispute without harming bilateral ties. Mr Trump also said he would visit Turkey, but added that a date had not been set yet. Mr Erdogan said earlier this week that the US president may visit in July.